The present invention relates generally to solenoid valves and more particularly to an electric vacuum regulator valve employing means for compensating for variations in magnetic force due to the change of resistivity of a coil.
Characteristic of all electromagnetic valves is a coil which upon energization develops magnetic flux used to move an armature. To insure the repeatability of the performance of such valves, it is necessary that the coil produce a constant magnetic flux under all operating conditions such that the electromagnetic force acting upon the armature is constant. Coils, of course, comprise a series of turns of wire and the resistance of this wire will vary depending upon the ambient temperature. Such change in resistance, while determinable, will cause an increase or decrease, as the case may be, in the coil current as function of temperature variation. As is known, the variation in the electromagnetic flux and force applied to the armature various in proportion with the change in current. Prior solenoid valves have attempted to compensate for changes in coil resistivity by way of electronics and more particularly by way of a constant current feedback circuit often located in series with a constrol signal generator and the coil. Those familiar with the state of electromagnetic actuators can appreciate that the cost of such constant current feedback circuitry often increases the cost of the solenoid valve three to four times.
It is an object of the present invention to provide a solenoid valve which produces a substantially constant magnetic field strength. A further object of the present invention is to provide a valve which is self regulating thereby avoiding the need for complicated circuitry as used in the prior art.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.
Accordingly, the invention comprises: a solenoid valve comprising: a stator; a coil responsive to current into thereto, for generating a nominal amount of magnetic flux and magnetically connected to the stator. The coil characterized such that its resistance changes with temperature to increase or decrease, as the case may be the amount of flux generated. A valve seat positioned about one end of the stator defining a valve seating surface positioned at a predetermined distance for the one end and a flat armature movable relative to the valve seat and when seated thereon is spaced from the one end. The armature including first means for causing a portion of such armature to move closer to or farther from the one end to vary the distance between such portion on the one end as a function of temperature to compensate for the changes in magnetic flux.